The invention described herein was made in the course of, or under, a contract with the U.S. Atomic Energy Commission.
1. Field of the Invention
This invention relates to fluid flow measuring devices, and more particularly to a device for measuring the flow of coolant entering the fuel bundles located in the core of a nuclear reactor.
2. Description of the Prior Art
The measurement of flow through fluid passages and particularly individual fuel subassemblies is of interest to reactor designers, operators, and safety review bodies for a variety of reasons, including establishing a maximum allowable power level, early determination of fuel assembly blockage due to crud deposits or obstructions, experimental design analysis and determination of other reactor parameters as stability and fuel temperatures. Passage as hereinafter used is defined as a path, channel, or course by which fluid passes. A problem associated with venturis and other devices as flowmeters is obtaining reliable differential pressure measurements. There must be either a suitable in-core differential pressure transducer to transmit a signal to a read-out device or long runs of tubing between the flowmeter and a differential pressure transducer located outside the reactor vessel.
The limitations of currently available pressure and differential pressure transducers for in-core applications is well documented in Chapter 4 of "Nuclear Reactor Instrumentation (in-core)" by James F. Boland, Argonne National Laboratory, ANS-USAEC Monograph Series on Nuclear Science and Technology, Gordan and Breach Science Publishers (1970).
The problems associated with long lines between flowmeters and differential pressure transducers include heat differentials, vapor or gas pockets in the lines, boiling or freezing fluids in the lines, poor time response and fluid temperature gradients. In addition, reactor applications have the additional plumbing problems of mechanical interference with fuel handling systems and high integrity seals where connecting lines exit from the reactor vessel. A large plurality of pressure differential lines magnifies the scope and impact of the above problems. Furthermore, reactor designers have long needed an accurate, reliable flowmeter for irregular shaped flow passages to determine precisely the flow rate within the passage which can change drastically as a function of changes in total reactor flow rate, viscosity, friction factors, flow patterns, heat generation rates, and mode of reactor loop operation.
The prior art shows various types of pressure differential flow measuring devices applicable to numerous types of uses. In "Shippingport Pressurized Water Reactor" presented at that second International Conference on the Peaceful Uses of Atomic Energy, Geneva 1958, the flow of coolant within square fuel assemblies of the Shippingport Pressurized Water Reactor was measured by modified venturis and flow nozzles located in fuel assembly support adapters. A disadvantage of this system in addition to those previously enumerated was the only 16 of 32 seed regions and 20 of 113 blanket regions were instrumented due to space limitations and fuel handling operations. Although representative positions were selected for instrumentation, the danger of loss of coolant flow in an uninstrumented fuel assembly remained a serious hazard. In addition, the flow nozzles resulted in higher pressure losses than venturi meters which measured coolant flow in the respective fuel channels.
U.S. Pat. No. 3,060,111 issued to J. Sherman et al on Oct. 23, 1962, alleviated some of the above problems in the Shippingport Reactor by instrumenting each individual seed and blanket assembly with a venturi flowmeter within the fuel assembly support structure. However, the solution resulted in the installation of 194 flow measuring tubes extending from the core, along and through the pressure vessel to recording instruments. This number of pressure lines required much precision bending and fabrication. More advanced Shippingport Reactor type concepts having fuel element cross sections other than square, such as U.S. Pat. Nos. 3,219,535 and 3,154,471 issued to T. R. Robbins and A. Radkowsky on Nov. 23, 1965 and Oct. 27, 1964 respectively, make little, if any, mention of the in-core coolant flow measurement instrumentation.
A further example of having individual venturis located at the entrance of each fuel assembly is U.S. Pat. No. 3,549,494 issued to J. H. Germer on Dec. 22, 1970. Again, precision tube fabrication and bending is required in order to implement the subject matter of the Germer invention.
Thus, it became apparent that the prior art flow measuring devices have been hampered by inaccurate measurement and pressure losses or required precision fabrication and bending of a large number of tubes. The problems inherent in pressure differential flow measuring devices remained unsolved and were further magnified by having a large number of pressure lines.
Thus, a need exists for a fluid flow measuring device having accurate flow measurement with low pressure losses that is simple and easy to install and maintain.